An acid based polymer electrolyte membrane (PEM) conducts protons from the anode to the cathode in PEM fuel cells more efficiently when the PEM is fully humidified. The PEM loses its ability to conduct protons as it dries under low relative humidity operations in PEM fuel cells. Attempts to develop acid based membranes with high acid loading have been made by reducing the membrane thickness and improving the water transport from the cathode to the anode. The designs attempt to make the PEM less dependent on humidification for efficient proton conduction. However, developing a membrane with high acid loading to improve the proton conductivity has been extremely challenging and expensive. And reduction in membrane thickness to improve the water transport from the cathode to the anode leads to compromise on membrane mechanical strength. In addition, reduction in membrane thickness proportionally increases the crossover rate of hydrogen from the anode to the cathode and oxygen from the cathode to the anode, adversely affecting the durability of the membrane and the electrocatalyst.
To overcome membrane dehydration and maintain the ionic conductivity, PEM fuel cell stacks can employ external humidifiers on both the anode and the cathode to humidify the anode feed gas and cathode oxidant. However, these external humidifiers add cost, complexity, and operational challenges to the PEMFC system and reduce system reliability.